MGB & GT Forum

Hello-
I am in the middle of preparing a black label overdrive that will be installed in my 73B. I have no history of this gearbox, so I began by replacing the OD O-rings, filters, gaskets, etc. I also replaced the seals at both ends of the gearbox, and the shims behind the front plate. Pretty standard stuff, and no problems.

Last night, I filled it with 30W non-detergent oil and hooked it up to a big drill to test the gearbox and overdrive. After spinning it for 30 seconds or so, it didn't seem to be kicking in the OD as I applied power to the solenoid. So I removed the solenoid and applied direct 12V to it. The solenoid plunger does move a little -maybe 1/8"-1/4" -but with very little force. With power applied, I can easily push it back into the coil- kind of like pushing against a light spring? Does this seem normal for the solenoid?

Secondly, and more concerning, is that now if the box is in any gear and I try to spin the input shaft backwards (CCW), it will not turn. It will go maybe 15 degrees and then come to a soft stop- feeling like I'm pushing against a spring. In correct rotation CW (drive)- it spins fine and correctly. Reverse is the opposite- spinning the input shaft in correct rotation (CW) will not spin the output flange CCW (soft stop again), but spinning the input backwards (CCW) spins the output flange in the forward drive direction (CW) just fine. With the box in neutral, the input shaft spins freely both directions. Prior to spinning it up with the drill, it spun fine by hand in either direction.

I have a spare gearbox that I checked and it spins freely in either direction when in gear.

I drained the oil, remove the side plate, OD plate, and solenoid to have a look around. I didn't see anything out of the ordinary.

Any ideas where to start looking? I'm seeing a complete tear-down of this box in my future unfortunately.



Edited 1 time(s). Last edit at 2015-11-25 07:43 AM by MGBInTheGarage.

The solenoid plunger should really snap with force extended.
Did you get the rpm up enough to reach pressure 420psi

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1957 Series 1 Land Rover electric VEHICLE CONVERSION

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Thanks for the solenoid info- I'll look into it.

I don't know about pressures- unfortunately I did not have a gauge (nor do I even own one that goes that high) connected during the test. I spun the input shaft up to 2000 rpm approx.
I also verified visually that the oil pump is operating correctly on the cam, and all O-rings are new.

part no 1003 LH Type Oil Pressure Gauge Set complete $49.50
James 630 653 0610

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LNDRVR4X4.COM
Home of Project "INCARN8'


1957 Series 1 Land Rover electric VEHICLE CONVERSION

FIXITUPCHAP.COM
FIXITUPCHAP INCORPORATED

RD3 Radar/ Electronic Warfare Technician
VIETNAM 1969-1972

One thought, it might be possible that the OD-unit is stuck in overdrive mode, that would keep it from spinning backwards.

A test: mark the input and output shafts with a reference mark, hand spin the input shaft counting rotations, if the OD is disengaged you should get the same ratio as your non-OD box on the output shaft; the OD ratio if overdrive engaged.

Whatever you do don't force it.

Thank you- sounds like a good price.

Thanks Clay- I'll look into that this evening.

I obtained an OD unit of unknown functionality, and I tried to test it with a powerful drill as you did. Although I couldn't get the OD to engage with the drill, it worked fine in the car. The drill just couldn't develop the RPM to build up enough pressure for the engagement to occur.

However, it sounds like you may have other issues as well - just don't put too much worry into it not engaging on the test bench.

Good point about the possibility of OD being stuck on and it ties in with the OP's comments about the OD not kicking in however with it out of the car it's it's hard to conceive of applying sufficient force to a stuck OD to physically damage it !

As it happens I've experienced a lock up similar to that reported and it was due to clinging baulk rings, I use 'clinging' to avoid having to say that they were stuck because they weren't..

On one gearbox I rebuilt using using salvaged parts, including a couple of perfectly serviceable baulk rings, after running through the gears on the bench I found it apparently locked and on removing the side cover discovered the reason to be that two baulk rings had 'clung' to their respective cones after the gear had been deselected effectively 'selecting' two gears simultaneously.

The 'cling' was tight enough to resist hand turning of the input shaft or output flange but only required a very small amount of assistance to release them, a screwdriver across the rear flange captive bolts in fact.

Having established that I chose to ignore it on the basis that in the car you have two rather substantial forces working to overcome such a issue, i.e. the input from the engine and the drive through the prop shaft when the car moves.

My decision was wholly vindicated when the gearbox worked perfectly in the car.

Thank Ernie. I have a question: I am certainly no expert in anything, but if I had balk ring problems, would the 4 speeds all work correctly in forward like mine do? My problems arise if I have the box in any gear and try to turn the input (1st motion) shaft in the opposite direction of engine rotation (counterclockwise), or if I try to turn the input shaft in the correct direction (clockwise) with the gearbox in reverse. It gradually builds resistance over a few degrees or rotation until I can't turn it by hand anymore- not a hard stop.

It was quite a while ago John so I can't really remember the precise details of the whole sketch but it's difficult to see what, either in the box or the OD, could cause the sort of gradual bind up you describe.

Gday,
Hijack,sorry, is the o/d box fitted to the C the same box fitted to a B?

Thanks Mal. In .au

For all intents and purposes yes.

No

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LNDRVR4X4.COM
Home of Project "INCARN8'


1957 Series 1 Land Rover electric VEHICLE CONVERSION

FIXITUPCHAP.COM
FIXITUPCHAP INCORPORATED

RD3 Radar/ Electronic Warfare Technician
VIETNAM 1969-1972